1. Field of the Invention
The present invention relates to an autofocus actuator, and more specifically to an autofocus actuator that can be employed in digital cameras or other small-sized electronic apparatuses equipped with a camera, e.g., cellular phones.
2. Description of the Related Art
In digital cameras, an actuator that can displace a lens in an optical axis direction is employed for the sake of autofocusing and zooming operations. This type of actuator is adapted to displace the lens in the optical axis direction by virtue of an interaction between the magnetic field generated by the electricity flowing through a coil and the magnetic field of a permanent magnet. In recent years, a need exists for the function of autofocus even in a camera mounted to cellular phones, because the number of pixels of a picture-taking element for use in the cellular phone camera tends to increase up to the order of mega pixels greater than one million.
One example of conventional autofocus actuators is disclosed in Japanese Patent Laid-open Publication No. 2003-295033. This autofocus actuator is comprised of a front lens, a front support frame for supporting the front lens, a front coil attached to the front support frame, a front spring affixed to the front support frame, a rear lens, a rear support frame for supporting the rear lens, a rear coil attached to the rear support frame, a rear spring affixed to the rear support frame, a magnet, a magnet support member and a yoke. The front coil is disposed in the outer gap between the magnet and the yoke, while the rear coil is located in the inner gap between the magnet and the yoke. Applying electric current to the front coil enables the front lens to move into a position where the front lens keeps in balance with the resilient force of the front spring. Likewise, applying electric current to the rear coil can bring the rear lens into a position where the rear lens keeps in balance with the resilient force of the rear spring.
The conventional actuator referred to above is of such construction that electricity is supplied to the coils via the front spring and the rear spring. This means that electrode portions for the coils and the power source should be provided on the front spring and the rear spring, respectively. In order to form such electrode portions, the front spring and the rear spring have to be subjected to bending process. A need of such bending process reduces the yield rate or productivity of the springs.
Furthermore, it is necessary to insulate the springs from other components due to the fact that coils or lead wires are directly soldered to the springs themselves for electric connection. This poses a drawback in that the number of parts of the actuator is increased.
Moreover, the front spring and the rear spring are of mutually different shape, which disadvantageously leads to an increased manufacturing cost of the springs.
In order to solve the problems noted above, the inventor of the subject application has conceived an autofocus actuator as illustrated in FIGS. 1 through 14.
The problems existed in the conventional actuators can be overcome by the actuator shown in FIGS. 1 to 14. However, both in the conventional actuators described above and the actuator shown in FIGS. 1 to 14, the yoke is formed into a cylindrical shape. In accordance with the contour of the yoke, each of the permanent magnets to be housed or mounted in the yoke is also necessary to have a shape curved in the form of an arc. However, the permanent magnets with such configuration are costly, thus the cost for the parts becomes higher.
In addition, the actuator referred to hereinabove requires the use of a gig or the like in the process of assembly to align the curved permanent magnets with respect to the yoke, thus making the assembly process troublesome.
Further, there is a need for providing a magnet support means or the like which can position the permanent magnets in advance into the yoke, which causes a problem in that the number of parts of the actuator is increased.